Abstract We report on the fabrication of dual-line waveguides with low propagation losses and single-mode guidance in Pr:CaF2 crystals by applying femtosecond laser inscription. In contrast to the typical highly elliptic modes previously reported in dual-line waveguides, the guiding mode obtained in our work is highly-localized with a near-circular profile at wavelength of 633 nm. The investigations on confocal micro-photoluminescence and micro-Raman imaging enable us to illustrate the effect of different femtosecond laser filamentations on the localized refractive index change in Pr:CaF2 crystals. In company with the mode simulation by finite element method, we further reconstruct the refractive index distribution of the fabricated waveguides. Our results indicate that highly-localized refractive-index increment caused by compressive stress between the lower parts of the filaments is the main mechanism for waveguiding, whereas the damage-induced refractive-index reductions at filaments and in the region between the upper parts of the filaments are responsible for the strong light confinement in both horizontal and vertical directions.

中文翻译：

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飞秒激光刻印 Pr:CaF2 波导：微光谱表征和折射率重建

摘要 我们报告了通过应用飞秒激光刻字在 Pr:CaF2 晶体中制造具有低传播损耗和单模引导的双线波导。与先前在双线波导中报道的典型高度椭圆模式相比，我们工作中获得的引导模式在 633 nm 波长处具有近圆形轮廓高度局部化。对共焦微光致发光和微拉曼成像的研究使我们能够说明不同飞秒激光灯丝对 Pr:CaF2 晶体局部折射率变化的影响。结合有限元方法的模式模拟，我们进一步重建了制造的波导的折射率分布。